The invention relates to a compressor according to the displacement principle for charging internal combustion (I.C) engines.
Exhaust gas turbocharging of I.C. engines as well as charging with compressors which operate according to the displacement principle is today's state of the art.
Nevertheless, exhaust gas turbochargers, mechanically driven turbochargers as well as compressors, which operate on the basis of the displacement principle, for example as exhaust gas screw chargers or screw chargers have some disadvantages:
to achieve the required pressure ratio high circumferential speeds are necessary. For the that reason, the charging effect is very low when starting the engine ("turbo hole")
at lower I.C. engine power only moderate degrees of efficiency are achieved, especially in partial load operation
the operating limit is given by the pumping limit of the compressor
the operating characteristic which increases steeply with speed has an unfavorable effect on the torque response of the I.C. engine which can only be improved with costly measures (blowing off exhaust gases or charging air, charging pressure regulation).
The advantage is that the exhaust gas turbo chargers take the entire energy required for compressing the charging air from the exhaust stream.
The advantages of displacement principal (Kv) charging units consists in that
even at low speeds it has a high pressure ratio for charging
it has no pump or surge limit
it has high degrees of partial load efficiency and an operating characteristic which is flat with the engine speed
this achieves also at low engine outputs high degrees of efficiency.
The disadvantage of the displacement principal charging unit consists in that the energy required for driving the compressor is taken from the I.C. engine over the entire operating range (mechanical coupling with the engine).
This disadvantage is met, for example in the exhaust gas screw charger in that through a screw expander (-engine) a part of the exhaust gas energy is gained back and again supplied to the screw charger via the mechanical coupling of screw expander and charger.
The disadvantage of this exhaust gas screw charger, however, lies in that
the screw expander has a relatively large constructional volume
low play must be retained at low and high exhaust temperatures
the screw expander can only be manufactured at high manufacturing costs.